Organic EL display devices are of a self light emitting type to be excellent in visibility, and are required to have no backlight to be capable of being made thin and light. Moreover, the display devices have a simple structure so that the display devices can be expected to be decreased in costs, and are also suitable for displaying moving images. In recent years, therefore, researches and developments about the display devices, and the commercialization thereof have been advanced as flat display devices (also referred to as flat panels) that follow liquid crystal display devices and plasma display devices.
The manner for attaining the full-color-display of organic EL display devices are roughly classified to a color filter manner, a different-color-separately-painted manner, and a color conversion manner. The color filter manner is a manner of combining a white-light-emitting organic EL element with a color filter, and the different-color-separately-painted manner is a manner of arranging respective light emitting layers in multiple colors such as red, green and blue into a planar form. The color conversion manner is a manner of combining an organic EL element that emits blue light with a color conversion layer. In the different-color-separately-painted manner, a color filter may be used together to heighten the purities of colors.
As illustrated in FIG. 11A, an organic EL display device of a white-light-emitting type in which organic EL elements (also referred to as organic light emitting elements or organic EL light emitting elements) 122 that emit white light are used is usually in a form of having not only pixels (also referred to as colored pixels) in which color-filter-forming coloring layers 113R, 113G and 113B having R, G and B colors, respectively, are arranged but also highly light-transmitting pixels high in light transmission property (white pixels in which a white layer 113W is arranged).
As illustrated in FIG. 11B, the display device may be in a form of arranging a circularly polarizing plate 130 onto on the front surface (observer side) of the white-light-emitting type organic EL display device to decrease the reflection of incident light rays from the outside.
Alternatively, as illustrated in FIG. 11C, the display device may be in a form of arranging a layer made of a light sensitive resin in which a colorant is dispersed in regions corresponding to the white pixels, and using this layer as transmittance adjusting portions 113WA to adjust the incidence of external light, and the reflection of the incident-made external light onto electrodes and metal wirings that the organic EL elements have (see Patent Literature 2).
Incidentally, reference signs or numbers in FIGS. 11A to 11C will be described in “Reference Signs List” that will be shown later.
In the case of the organic EL display device illustrated in FIG. 11A, the reflectivity of external light made incident from the front surface (observer side) is usually about 97%.
In the case of the organic EL display device illustrated in FIG. 11B, the reflectivity of external light made incident from the front surface (observer side) is usually about 0.1%. The display brightness thereof is about 40% of that of the organic EL display device in the form illustrated in FIG. 11A.
In the case of the organic EL display device in FIG. 11C, the transmittance adjusting portions 113WA make it possible to adjust the incidence of external light, and the reflection of the incident-made external light onto electrodes and metal wirings that the organic EL elements have. However, the reflection of the external light is insufficiently decreased, and unevenness in the reflection is easily viewed.
Usually, in the highly light-transmitting pixels, an uncolored resin layer is arranged, or a resin layer slightly colored to be matched with a color obtained by combining R, G and B colors with each other is arranged. Such highly light-transmitting pixels are referred to as white pixels, and the resin layer arranged in the white pixels is referred to as a white layer 113W.
Any organic EL display device may be referred to as an organic electroluminescence display unit or organic EL displaying device, and any display device may be referred to as a display panel.
As described above, white-light-emitting type organic EL display devices, in which white-light-emitting organic EL elements are used, are in various forms. In any one of the forms, a white-light-emitting organic EL element is arranged correspondingly to each of its pixels, and the pixel is controlled and driven through a TFT element. However, in any of the forms, at the time of paying attention to some pixel region of its pixel regions, white light from an organic EL element for displaying a pixel adjacent to the pixel region directly enters the coloring layer of the pixel region, or white light from an organic EL element for displaying a pixel adjacent to the pixel region passes through a color-filter-forming coloring layer of this adjacent pixel to enter the coloring layer of the pixel region. This matter causes color shift or color mixing in an image displayed (in the pixel region) in accordance with the direction in which the image is viewed.
This is caused since entire light rays from the organic EL elements are not radiated into the color filter forming substrate along a direction perpendicular to the plane of its substrate, so that the rays are radiated thereinto to have broad incident angles.
When white light from the organic EL element for displaying some pixel of the pixels passes through the color-filter-forming coloring layer of the pixel to enter the coloring layer of a pixel adjacent to the pixel, almost the entire white light is absorbed (in these pixels) in accordance with the respective light transmission properties of the two coloring layers in the visible light band. Thus, in particular, the matter that the white light from the organic EL element for displaying the (image-displayed) pixel directly enters into the coloring layer of the pixel adjacent thereto largely affects color shift or color mixing of the displayed image.
Also in a different-color-separately-painted type organic EL display device, which has organic EL elements in which respective light emitting layers in multiple colors such as red, green and blue are arranged in a planar form, at the time of using a color filter together therewith, color shift or color mixing is generated in an image displayed therein in the same manner as in the above-mentioned white-light-emitting type organic EL display device.
FIG. 15 is a graph showing an example of the following: emission spectra of an organic EL element in which respective light emitting layers in three colors of red, green and blue are arranged in a planar form; and transmission spectra of a color filter. For example, the emission spectrum of the blue light emitting layer of the organic EL element partially overlaps the transmission spectrum of a green coloring layer of the color filter, so that blue light from the blue light emitting layer partially transmits the green coloring layer. Similarly, the emission spectrum of the green light emitting layer of the organic EL element partially overlaps the transmission spectrum of a blue coloring layer of the color filter, so that green light from the green light emitting layer partially transmits the blue coloring layer. Furthermore, the emission spectrum of the red light emitting layer of the organic EL element partially overlaps the transmission spectrum of the green coloring layer of the color filter, so that red light from the red light emitting layer partially transmits the green coloring layer. For this reason, color shift or color mixing is unfavorably caused in the image displayed by a matter that light from the organic EL element of a pixel adjacent thereto enters the (image-displayed) pixel.
Following requests for making displays highly minute and fine, and making the quality thereof high, it has been becoming impossible, about each of the pixels, for the quality of the pixel, to ignore the entry of light into the pixel from the organic EL element of a pixel adjacent to the pixel.